Integrated circuits (ICs) for controlling electronic devices, such as disk drives, are typically cut from silicon wafers and packaged so that they can be electrically attached to circuitry of a printed circuit board (PCB). The top surface of the PCB typically includes electrical contacts to which terminals of the IC package may be connected. As technology moves forward, ICs are designed to carry out more functions of greater complexity. As a result, the number of electrical contact points for power supply and input/output (I/O) signals to and from ICs continues to increase. IC packages that can handle an increased number of electrical contact points are therefore required. Ball grid array (BGA) packages, which utilize solder balls on their mounting surfaces instead of pins for mounting to PCB contacts, are especially useful because they allow for more contacts per unit package area.
One of the major factors that limit the performance of data storage devices, such as disc drives, is the speed at which digital data can be communicated between the drive and another device, such as a computer bus. One of the ways to increase total speed is to transmit more data bits in parallel. Protocols such as SCSI (small computer system interface), wide SCSI, and ultra wide SCSI have taken this route to the point where data synchronization and the shear physical size of the cables limit further gains. Recent interest has focused upon the opposite extreme: single-bit serial communications at base data rates in the ultrahigh and extremely high frequency range. For example, high-speed differential signals, including Fiber Channel signals or other serial signals such as Serial Attached SCSI (SAS) signals or Serial Advanced Technology Attachment (SATA) signals, propagate data at speeds of 4.25 Gbit/s and above.
Successful transmission of high-speed differential signals to and from ICs within data storage devices requires low-loss transmission lines with minimal parasitic inductance and capacitance. In a BGA package, wire bonds electrically couple a set of signal contacts disposed near an outer edge of the BGA package to an IC mounted on the BGA package. The long wire bonds used to transmit high-speed differential signals between the BGA package and the IC include excess parasitic inductance that may reduce the quality and signal edge rate of the high-speed differential signals. High performance packages may use flip chip attachments to reduce this parasitic effect. However, the flip chip technique is more expensive than wire bonding and is not a viable solution for cost sensitive applications.
Furthermore, some storage device ICs may include an analog circuit that requires isolated connectivity of the power and ground bus to reduce noise in the analog circuit from the rest of the circuits in the IC. For example, connecting analog power to common BGA package power rings may substantially increase an amount of noise in the analog circuit of the IC. Therefore, an analog circuit of the IC may connect to external power through a set of isolated power contacts located near an edge of a BGA package. However, since long bond wires are used to couple the set of power contacts to the IC, the isolation of these analog connections results in more inductance in the BGA package interconnects. The inductance within the wire bonds may also lead to higher noise on the IC due to activity in the analog circuit as transient power supply voltage noise amplitude is proportional to inductance, i.e., V=−L*(di/dt).